Human exposure to industrial chemical compounds is widespread and, although often beneficial, prolonged contact may contribute to disease development, including cancer. While many studies have shown organic pollutants (OP) are cytotoxic, few have explored how long‐term exposure alters cell phenotype. Therefore, the current study investigated whether exposure to the OP perfluorooctanoic acid (Pfoa: 0.01, 0.1, and 1 μM), bisphenol A (Bpa: 0.1 and 1 μM), methoxychlor (Mtx: 0.1 and 1 μM), and benzophenone‐1 (Bp1: 1 and 10 μM) modulates the phenotype of MCF7 human breast cancer cells and MCF10A normal breast epithelial cells. MCF7 cells were exposed to environmentally relevant concentrations of the OP for 24 h and 15 days. Cell viability, proliferation, colony formation, drug‐efflux activity, and gene expression were assessed. A modulation of MCF7 breast cancer cell phenotype was observed, with increased proliferation and colony formation (Pfoa, Bpa, Mtx, Bp‐1), particularly at 15‐day exposure and with expression of genes involved in cell survival, proliferation, differentiation, and chemoresistance (STAT3 and VEGFA [Bpa, Mtx, Bp‐1], BRCA1 [Bp1], ESR2 [Pfoa, Bpa], ABCG2 [Pfoa]). No effects on cell migration and drug‐efflux activity were observed. Likewise, an increase in cell proliferation also occurred for MCF10A nontumor cells (Bpa, Mtx, Bp‐1), but these effects were usually less pronounced than those observed in MCF7 cells. Pan‐cancer analysis revealed a negative correlation between the expression of STAT3, VEGFA, ESR2, and ABCG2 and breast cancer patient survival. These findings suggest that low‐concentration, prolonged exposure to OP may promote tumor progression and aggressiveness in breast cancer, potentially undermining therapeutic outcomes.

Gold (AuNP) and silver (AgNP) nanoparticles have been incorporated into many therapeutic and diagnostic applications. However, previous studies revealed toxic properties as well as hormesis phenomenon of many nanoparticles in different biological models. To evaluate the effects of low concentrations of AuNP and AgNP on murine melanoma cells B16F1 and B16F10 and relate them with phenotype changes, cells were exposed for 24 and 48h. No cytotoxicity was observed for B16 cells through neutral red, MTT, trypan blue and crystal violet assays at concentrations from 0.01 to 10 ng mL⁻¹. Likewise, the nanoparticles did not interfere with drug-efflux activity, cell migration, cell cycle and colony formation. Slight toxicity was observed for B16F10 exposed to 100 ng mL⁻¹, with decreased number of viable and attached cells, indicating differential sensitivity of B16F1 and B16F10 cells to the nanoparticles. Furthermore, colony size dispersion decreased for both B16 cell sub-lines. Therefore, there is no evidence that the tested concentrations of AuNP and AgNP can render B16 cells more aggressive and malignant, which is important since both nanoparticles are already largely used in nanotechnological products. Considering studies that have showed hormesis effect of nanoparticles at low concentrations, which could protect cancer cells against chemotherapy, further investigation is advised.